Cleanup dead code in base/ as found by Scythe.

base/process/process_metrics.h

Index: base/process/process_metrics.h
diff --git a/base/process/process_metrics.h b/base/process/process_metrics.h
index d06e018e6074638edbfe09f8f767021339c596a7..d011958eb0e1eef02dd9d134bb8371a27aa6c4e0 100644
--- a/base/process/process_metrics.h
+++ b/base/process/process_metrics.h
@@ -85,17 +85,6 @@ struct CommittedKBytes {
   size_t image;
 };
 
-// Free memory (Megabytes marked as free) in the 2G process address space.
-// total : total amount in megabytes marked as free. Maximum value is 2048.
-// largest : size of the largest contiguous amount of memory found. It is
-//   always smaller or equal to FreeMBytes::total.
-// largest_ptr: starting address of the largest memory block.
-struct FreeMBytes {
-  size_t total;
-  size_t largest;
-  void* largest_ptr;
-};
-
 // Convert a POSIX timeval to microseconds.
 BASE_EXPORT int64 TimeValToMicroseconds(const struct timeval& tv);